PRODUCTION D'ORGANOBORANES OPTIQUEMENT PURS

PRODUCTION OF OPTICALLY PURE ORGANOBORANES

Abrégé anglais

Abstract
A process for upgrading to essentially 100%
enantiomeric excess the optical purity of an organoborane
intermediate represented by the formulae:
IpCBHR* or Ipc2BR*
wherein Ipc is isopinocampheyl and R* is a unsubstituted or
substituted, acyclic or cyclic alkyl having from 4 to 30
carbon atoms, compri,sing the steps of hydroborating cis-
alkene, a trans-alkene or a tertiary-alkene with mono-
isopinocampheylborane or diisopinocampheylborane, obtaining
a solid organoborane and recrystallizing the solid
organoborane to obtain an enantiomeric excess of essentially
100% ee of said organoborane.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for upgrading to essentially 100%
enantiomeric excess the optical purity of an organoborane
intermediate represented by the formulae:
IpcBHR* or Ipc2BR*
wherein Ipc is isopinocampheyl, and R* is a substituted or
unsubstituted cyclic or acyclic alkyl having from 4 to 30
carbon atoms comprising the steps of :
a) reacting an alkene selected from the group
consisting of a cis-alkene, trans-alkene or tertiary-alkene
with a hydroborating agent selected from the group
consisting of monoisopinocampheylborane and
diisopinocampheylborane;
b) obtaining a solid intermediate; and
c) recrystallizing the resulting solid
hydroboration product from a suitable solvent to obtain a
monoisopinocampheylalkylborane or diisopinocampheylalkyl-
borane of essentially 100% enantiomeric excess.
2. The process of claim 1 wherein said
hydroboration product is recrystallized from a hydrocarbon
or an ether solvent.
3. The process of claim 1 wherein said hydrocarbon
solvent is pentane.
4. The process of claim 2 wherein said solvent is
diethyl ether.
28 ,

5. A process for upgrading to essentially 100%
enantiomeric excess the optical purity of an organoborane
intermediate represented by the formula:
IpcBHR*
wherein Ipc is isopinocampheyl, and R* is a substituted or
unsubstituted, cyclic or acyclic alkyl having from 4 to 30
carbon atoms comprising the steps of :
a) reacting a trans-alkene or a tertiary-alkene
with monoisopinocampheylborane; and
b) obtaining a solid intermediate; and
c) recrystallizing the resulting hydroboration
product from a suitable solvent to obtain a
monoisopinocampheylalkylborane of essentially 100 %
enantiomeric excess.
6. The process of Claim 5 wherein said
hydroboration product is recrystallized in a hydrocarbon or
an ether solvent.
7. The process of Claim 6 wherein said hydrocarbon
solvent is pentane.
8. The process of Claim 6 wherein said ether
solvent is diethyl ether.
9. A recrystallized monoisopinocampheylalkyl-
borane of essentially 100% enantiomeric excess prepared by
the process of Claim 1, represented by the formula
IpCBHR*
29

wherein Ipc is isopinocampheyl and R* is an unsubstituted or
substituted, cyclic or acyclic alkyl having from 4 to 30
carbon atoms.
10. A process for upgrading to essentially 100%
enantiomeric excess the optical purity of an organoborane
intermediate prepared by hydroborating a cis-alkene with
diisopinocampheylborane and represented by the formula
Ipc2BR*
wherein Ipc is isopinocampheyl, and R* is an unsubstituted or
substituted acyclic or cyclic alkyl having from 4 to 30
carbon atoms represented by the formula
<IMG>
where the .alpha. -carbon is a new chiral center and where R1 and
R2 are the same or different members of the group
consisting of straight or branched chain, substituted or
unsubstituted alkyl, unsubstituted or substituted cycloalkyl
and aryl, said process comprising the steps of :
a) reacting a cis-alkene with diisopinocampheyl-
borane;
b) obtaining a solid organoborane; and
c) recrystallizing said solid organoborane from a
suitable solvent.

11. The process of Claim 10 wherein said solvent
is a hydrocarbon or an ether solvent.
12. The process of Claim 11 wherein said
hydrocarbon solvent is pentane.
13. The process of Claim 11 wherein said ether
solvent is diethyl ether.
14. A process for upgrading to essentially 100%
enantiomeric excess the optical purity of organoborane
intermediates prepared by hydroborating a cis-alkene with
diisopinocampheylborane and represented by the formula:
Ipc2BR*
wherein Ipc is isopinocampheyl and R* is
<IMG>
where the .alpha.-carbon is a new chiral center and where R1 and
R2 are the same or different members of the group
consisting of straight or branched chain, substituted or
unsubstituted alkyl, unsubstituted or substituted cycloalkyl
and aryl, said process comprising the steps of:
a) reacting a cis-alkene with diisopinocampheyl-
borane to obtain a non-solid hydroboration product;
b) converting said non-solid borane to a solid
compound selected from the group consisting of a borate, a
borane complex and a chelate by treatment with a compound
selected from the group consisting of a strong base, an amine
having low steric requirements and an aminoethanol chelating
agent; and
c) recrystallizing said solid from a suitable solvent
to obtain a diisopinocampheylalkylborane of essentially 100%
enantiomeric excess.
31

15. The process of claim 14 wherein said
non-solid borane is converted to a solid borate.
16. The process of Claim 14 wherein said
non-solid borane is converted to a solid borate by
treatment with a strong base.
17. The process of Claim 16 wherein said strong
base is an alkali metal base.
18. The process of Claim 14 wherein said
non-solid borane is converted to a solid borane complex.
19 . The process of Claim 14 wherein said
non-solid borane is converted to a solid borane complex by
treatment with an amine having low steric requirements.
20. The process of Claim 18 wherein said
non-solid borane is converted to a borinic acid by treatment
with an equivalent of aldehyde and the borinic ester is
converted to a solid chelate.
21. The process of Claim 20 wherein said
non-solid borane is converted to a solid chelate by
treatment of said borinic ester with an aminoethanol
chelating agent.
22. The process of claim 21 wherein said
aminoethyl chelating agent is selected from the group
consisting of ethanolamine, N-methylethanolamine, 2-
pyrrolidinemethanol and 2-pyridyl-2-methanol.
32

23. A borane intermediate of essentially 100%
enantiomeric excess prepared by recrystallization by the
process of claim 1 and represented by the formula:
Ipc2R*B
wherein Ipc is isopinocampheyl and R* is
<IMG>
where the .alpha.-carbon is a new chiral center and where R1 and R2
are the same or different members of the group consisisting
of straight or branched chain, substituted or unsubstituted
alkyl, unsubstituted or substituted cycloalkyl and aryl.
24. A process for upgrading to essentially 100%
enantiomeric excess the optical purity of organoborane
intermediates prepared by hydroborating a trans-alkene or
tertiary-alkene with monoisopinocampheylborane and
represented by the formula:
IpcBHR*
wherein Ipc is isopinocampheyl and R* is a straight or
branched chain, substituted or unsubstituted alkyl,
unsubstituted or substituted cycloalkyl or aryl, said
process comprising the steps of:
a) reacting a trans-alkene or tertiary-alkene with
monoisopinocampheylborane to obtain a non-solid
hydroboration product;
33

b) converting said non-solid borane so obtained to
a solid selected from the group consisting of a borate, a
boron complex and a chelate by treatment with a compound
selected from the group consisting of a strong base, an
amine having low steric requirements and an aminoethyl
chelating agent; and
c) recrystallizing said solid from a suitable
solvent to obtain a monoisopinocampheylalkylborane of
essentially 100% enantiomeric excess.
25. The process of claim 24 wherein said
non-solid borane is converted to a solid borate.
26. The process of Claim 24 wherein said
non-solid borane is converted to a solid borate by
treatment with a strong base.
27. The process of Claim 26 wherein said strong
base is an alkali metal base.
28. The process of Claim 24 wherein said
non-solid borane is converted to a solid borane complex.
29. The process of Claim 24 wherein raid
non-solid borane is converted to a solid borane complex by
treatment with an amine having low steric requirements.
30. The process of Claim 28 wherein said
non-solid borane is converted to a borinic acid by treatment
with an equivalent of aldehyde and the borinic ester is
converted to a solid chelate.
31. The process of Claim 30 wherein said
non-solid borane is converted to a solid chelate by
treatment of said borinic ester with an aminoethanol
chelating agent.
34

32. The process of claim 31 wherein said
aminoethyl chelating agent is selected from the group
consisting of ethanolamine, N-methylethanolamine, 2-
pyrrolidinemethanol and 2-pyridyl-2-methanol.

Description

~265536
--1--
PRODUCTIt)N OF OPTICALLY PURE ORGANOBORANES
Back~round of the Invention
(I) Field of Invention
The present invention relates to an improved
method for converting organoboranes containing a partially
optically active organyl group attached to boron, and more
specifically relates to methods and intermediates for the
asymmetric hydroboration of cis-alkenes, trans-alkenes and
tertiarY-alkenes to organoboranes containing an
essentially optically. pure organyl group.
Asymmetric hydroboration of alkenes, with either
diisopinocampheylborane or monoisopinocampheylborane
typically provides the corresponding chiral organoborane
containing the new alkyl group, R*, in from 50 to 90~
enantiomeric excess (ee), and occasionally in purities of
from gO to 100~ ee. Because of the importance of
hydroboration to, for example, the pharmaceutical industry,
there has been a long standing need for a simple, reliable
process which provides the alkyl group, R*, in 100~ ee in
all cases. The present invention fulfill~ that need in cases
involving cis-alkenes, trans-alkenes, tertiarY-alkenes and
the hydroborating agents dlisopinocampheylborane and
monoisopinocampheylborane.
~II) Description of the Prior Art
The first successful asymmetric synthesis occured
in 1961 with the hydroboration of cis-2-butene in diglyme
(DG) by the chiral dialkylborane, diisopinocampheylborane to
.
~!s

~2~5536
' -2-
yield 2-butanol of 87% ee. Brown, H.C. et al., J. Am. Chem.
Soc. 86, 397 (1964). Diisopinocampheylborane (Ipc2BH) was
prepared by the hydroboration of (~)- and (~ -pinene. See
Brown, H.C. and Zweifel, G., J. Am. Chem. Soc., 83. 486
(1961). (FIG. l). That landmark achievement not only
provided a remarkably high asymmetric synthesis, the first
of its kin~, but further provided a reagent which appeared
generally applicable to the asymmetric hydroborat~on of
cis-alkenes. Brown, H.C. et al, JACS 86, 397 (1964) and
Partridge, J.J., et al, JACS 95, 532 (1973). (FIG. 2)
The chiral intermediate, 2-butyldiisopinocampheyl-
borane, was subsequently converted into optically active
2-aminobutane with complete retention of configuration and
into 2-iodobutane with complete inversion of configuration.
Verbit, L. et al, JOC 32, 3199 (1967) and Brown, H.C. et al,
JASC 98, 129~ (1976). (FIG. 3).
In the original study of hydroborations with
optically active diisopinocampheylborane, the reagent
employed was prepared from commercial o-pinene of relatively
Low enantiomeric purity ( ~ 93%). Subseguent advances
resulted in the preparation of reagent of high enantiomeric
purity from such a-pinene. The reagent is eguilibrated at
0~C with 15% excess ~-pinene. The major isomer becomes
incorporated into the crystalline reagent, leaving the minor
isomer in solution. Brown, H.C. et al, Israel J. Chem. 15,
12 (1977). (FIG. 4). Treatment of the diisopinocampheyl-
borane with benzaldehyde liberated a-pinene of
approxlmately 10D % ee. Thus, two reactions were developed
which provided a convenient procedure for upgrading the
commercial ~-pinene to an enantiomeric purity of
essentially 100% ee. Brown, H.C. et al, JOC 47, 4583 (1982).
(FIG. 5)
~Y

~265536
-3-
Improved asymmetric results were achieved in the
hydroboration of cis-alkenes with this improved reagent and
a somewhat lower hydroboration temperature (-25C). Brown,
.C. et al, JOC 47, 5065 (1982). (FIG. 6).
It has been found that while
diisopinocampheylborane (Ipc2BH) handles cis-alkenes very
effectively, it is not an effective asymmetric hydroborating
agent for trans-alkenes and trisubstituted alkenes and that
monoisopinocampheylborane (IpcBH2 )is a more effective
hydroborating agent for the latter types of alkenes.
It is difficult to halt the hydroboration of
~ -pinene at the monoalkylborane stage. Consequently, it was
found that the monoisopinocampheylborane must be prepared by
an indirect route, such as by treating diisopinocampheyl-
borane with one-half molar equivalent of N,N,N,N-
tetramethylethylenediamine (TMED) to obtain 2(1pcBH2).TMED.
The diastereomeric adduct crystallizes out in
enantiomerically pure form, and the pure
monoisopinocampheylborane is readily liberated by treating
the adduct with boron trifluoride etherate according to the
method of Brown, H.C. et al, JOC 43, 4395 (1978).
Monoisopinocampheylborane has been found to be
very effective for the asymmetric hydroboration of trans
-alkenes (See Brown, H.C. et al, JOC 46, 5047 (1981)(FIG.
10). Similarly, the hydroboration of trisubstituted alkenes
with monoisopinocampheylborane, followed by oxidation of the
~,. . ~j

~26553~
--4--
intermediate organoboranes, provides the corresponding
alcohols in 53-72% ee, Brown, H.C. et al, JACS 99, 5514
(1977); Brown, H.C. et al., JOC 47, 5074 ~1982) (FIG. 10).
For reasons that are not understood, the
asymmetric hydroboration of the phenyl derivatives provides
considerably improved hydroboration products of, for example
82~ ee, 85~ ee, 100~ ee and 88 % ee(FIG. 11) as compared to
the 53% ee, 62~ ee, 66~ ee and 72% ee respectively for the
corresponding parent compounds (FIG 10), see Mandal, A.K.
et al, JOC 45, 3543 (1980).
Monoisopinocampheylborane and diisopinocampheyl-
borane are complementary to each other, and are capable of
handling three of the four major classes of alkenes.
Diisopinocampheylborane, a reagent with larger steric
requirements, is more suited for use in the case of
unhindered cis-olefins. On the other hand, hydroboration of
olefins with larger steric requirements proceeds more
favorably with a reagent of lower steric requirements, mono-
isopinocampheylborane. ~here still remains a need for a
suitable reagent which will permit synthesis of products of
high enantiomeric excess from alkenes of relatively low
steric requirements, such as the 2-methyl-1-alkenes.
Initially, the application of chiral organoboranes
was limited primarily to alcohols because of the presence of
isopinocampheyl groups on boron in the product. Recently, it
was discovered that these groups can be selectively
eliminated by treatment of the mixed chiral organoboranes
with acetaldehyde, regenerating the ~-pinene, and providing
the optlcally active boronate as the product. In this way,
for example, 2-butyldiisopinocampheylborane is readily
converted into diethyl 2-butylboranate in 97% ee. Brown,
H.C. et al, JACS, 104, 4303 (1982). (FIG. 12)

~265536
--5--
Similarly, diethyl trans-2-phenylcyclopentyl-
boronate can be obtained in 100~ ee by the method of Brown,
H.C. et al, JACS 104, 4303(1982J. (FIG. 13).
Hydroboration of prochiral alkenes with diisopino-
c~mpheylborane and monoisopinocampheylborane typically
results in products in which approximately 60 to 90~ optical
activity is generally induced in the R*BIpc2 and R*BHIpc.
This means that the major isomer is p~esent in large
amounts, 80-95~, and the minor isomer in much smaller
amounts, 20-50~. The problem is how to separate the major
isomer from the small amount of minor isomer present.
The usual organic synthesis of enantiomers
produces a 50:50 mixture of the two optical isomers.
Normally, these are separated by combining them with
naturally occurring optically active acid or base (chiral
auxiliary) to form a pair of diastereoisomers. Laborious
fractional crystallization then separates the two
diastereoisomers. The chiral auxiliary is then removed to
regenerate the desired optically active compound.
However, it is not always possible to resolve
optical mixtures once the final products have been obtained
without destroying the molecule, and there has been a
longstanding nee~ for a reliable method of resolving the
mixture at a stage to obtain an optically pure inter~,edi~te
which can then be converted to any number of final products
while retaining its optical configuration.
It has now been discovered that optically pure
organoborane intermediates can be reliably and readily
obtained from trans-alkenes, tertiary-alkenes and
monoisopinocampheylborane or cis-alkenes and
diisopinocampheylborane by recrystallization of the
resulting boron intermediate if solid, or first converting

~26S5~
-6-
the liquid to a solid according to the process of the
present invention. The process of the present invention not
only eliminates the necessity of employiny a chiral
auxiliary to separate the diasteroisomers, but provides the
desired organyl yroups, R*, in essentially 1004ee.
Conseguently, the present method provides an advance in the
art. By the process of this invention, it is now possible to
prepare virtually any optically active compound with a
chiral center, either d- or 1-, in essentially 100~ ee. from
a cis-alkene, trans -alkene or dialkene.
Summar~ of the Disclosure
The present invention provides methods for
preparing optically pure organoboranes from cis-alkenes,
trans- or terti~-alkenes and diisopinocampheylborane or
monoisopinocampheylborane cont~ining the chir~l group R*
attached to boron in an optical purity of essentially 100~
ee. These optically pure organoboranes are then readily
converted into essentially any class of organic cosnpounds,
making possible the synthesis of a large number of
monochiral organic compounds in an optical purity of
essentially 100~ ee.
Brief Description of the Drawinas
~he invention will be more readily understood by
the following description, taken in conjuction with the
drawings in which:
FIG. 1 is a reaction scheme of the original
asymmetric hydroboration;
FIG. 2 is a reaction scheme of representative
asymmetric hydroboration of cl ~-alkenes;
FIG. 3 is a reaction scheme of representative
conversions of the chiral intermediate, 2-butyl-
diisopinocampheylborane to optically active 2-aminobutane
~r
~p~

~265~36
--7--
with complete retention~ of configuration and 2-iodobutane
with complete inversion of configuration and which is
applicable to many syntheses;
FIG. 4 is a reaction 6cheme of the preparation of
optically pure diisopinocampheylborane (100% ee);
FIG. 5 is a reaction scheme of a convenient
procedure for upgrading ~)- and (~ -pinene to material of
high optical pur,ity;
FIG. 6 depicts reaction schemes of representative
applications of 100~ pure diisopinocampheylborane to the
hydroboration-oxidation of cis-alkenes;
FIG. 7 depicts reaction schemes of representative
applications of 100~ pure diisopinocampheylborane to the
hydroboration-oxidation of heterocyclic olefins;
FIG. 8 is a reaction scheme of the preparation of
monoisopinocampheylborane of high optical purity;
FIG. 9 depicts reaction schemes of representative
applications of monoisopinocampheylborane to the
hydroboration-oxidation of tranS-alkenes;
FIG. 10 sets forth representative reaction schemes
for the hydroboration-oxidation of trisubtituted alkenes
with monoisopinocampheylborane;
FIG. 11 sets forth representative reaction schemes
for the hydroboration-oxidation of phenyl-substituted
alkenes;
FIG. 12 ''is a reaction scheme of the direct chiral
synthesis of boronic esters using diisopinocampheylboranes
and
FIG. 13 is a reaction scheme of the direct chiral
synthesis of boronic esters using monoisopinocampheylborane.
Detailed Description of Preferred Embodiments
The present invention provid,es a simple, direct
and economical method of prnducing,,an optically pure boron
~I Y
.

--8--
intermediate which can be converted to virtually ~ny
optically active compound having a chiral center, either d-
or 1-, in essentially 10~4 enantiomeric exce~s. The process
of the present invention eliminates the neces~-ity of
undertaking laborious fractional crystallization to obtain
the desired diasterioisomer.
In one aspect, the proces~ of this invention
comprises the producing in essentially 100~ enantio~eric
excess (ee) an optically pure organoborane comprising the
steps of re~cting a cis-alkene with the optically active
hydroborating agent diisopinocampheylborane, or a trans- or
tertiary-alkene with monoisopinocampheylborane, obtaining a
~olid hydroboration product and recrystallizing said solid
hydroboration product from a suitable reagent at low
temperature.
In cases where the organoborane resulting from the
reaction of a prochiral al~ene and the optically dCtiVe
hydroborating agent is a solid, simple recrystallization of
the reaction product, with, for example, a hydrocarbon such
as pentane or ether, results in the desired organoborane
intermediate of essentially 100~ enantiomeric excess.
In cases where the.organoborane~ is a liguid, a
solid derivative is prepared by forming either a crystalline
borate, a borane complex or a chelate.
Crystalline borates are conveniently obtained by
treating the liquid organoborane, Ipc2BR*, with a strong
base preferably an alkali metal base such as such as LiMe,
LiH, LiNMe~ , KOMe, KCNI illustrated in the following
3~ reaction schemes.
Ipc2BR* + MX ~- M[Ipc2BR~X]
wherein M is an alkali metal and X is selected from the
group consisting of hydrogen, lower alkyl, lower alkoxy, CN,

~L265S36
g
NRlR 2 wherein R~ and R 2 are the same ~r different members of
the group consisting of hydrogen and lower alkyl.
Crystalline borane complexes are readily prepared
by reacting the liquid organoborane with an amine of low
steric reguiremen~s such as ammonia, methylamine, dimethyl-
amine, trimethylamine, pyrrolidine, piperidine, and the
like, according to the following reaction~ schemes:
Ipc2BR* ~ (CH3)3N ~ IpC2R*B N(C~3)3
Ipc2BR* ~ Py
wherein Py is pyridine, etc.
Solid chelate deriv~tives are prepared by reacting
the liquid organoborane with an aldehyde to form the borinic
acid ester, followed by a suitable chelating agent such as
ethanolamine, N-methylethanolamine, 2-pyridylmethanol,
2-pyrrolidinemethanol and similar chelating ayents as
represented by the following formulae:
Ipc2R~B + R'CHO ~ IpcR*BOR' + ~-pinene
I~c ~O---C~2
\/ ; `
IpcR~OR' + H2NCH2CH20H ~ ~ ~
R ~H2 CH
Ipc O~
IpcR~BOR' + ~ ~ /
CH2~ R* ~ ~
~)J,
....... .: ,,
.

~2~S536
The term ~suitable aminoethanol chelating agent
refers to compounds represented by the formula RN~CH2C~2O~
where R consists of hydrogen, Cl to C6 straight or b~anched
chain alkyl and C3 and C6 cycloalkyl and benzyl.
Alternatively, the liquid hydroboration products,
Ipc2 BR* can be enr~ched by selective treatment with an
appropriate reagent which preferentially destroys one
isomer, permi~ting an enrichment in the less reactive
isomer. This procedure takes advantage of the fact that such
compounds contain three dif ferent optically active groups.
They will therefore exist of at least two differ~nt
diastereomers with different reactivities. The enrichment
with aldehydes, preferably benzaldehyde, is valuable for
such enrichments which proceed according to the following
general reaction scheme.
Ipc~BR* t C6H5C~O- ~ IpcR~gocH2C6H5 ~ ~-pinene
Enrichn,ent may also be achieved by carrying out
the displacement to produce a mixture of borinic and boronic
esters which are readily separated by selective extraction
with alk~li. The borinic acid is isolated, converted to the
methyl ester or trimethylene glycol ester, for example, or
oxidized to the alcohol.
In cases where the reaction product of an alkene
with monoisopinoc~mpheylborane or diisopinocampheylborane is
a solid; direct crystallization by treatment with a suitable
solvent, preferably a hydrocarbon such a5 n-p~ntane,
iso-pentane, or hexane, or an ether such as diethyl ether,
tetrahydrofuran or dimethoxyethane, result in the desired
crystalline intermediate havi~ an enantion~eric purity in
excess of 98~ee.

126~i5~36
--11--
In cases where the reaction product of an alkene
with either monoisopinocampheylborane or
diisopinocampheylborane is a liquid, e.g. an oil, it is
first necessary to convert the reaction product to a solid
as described above. The solid borate, borane complex or
chelate is then recrystallized by treatment with a suitable
solvent to obtain the desired borane intermediate of 98% or
greater ee.
As used herein, the term "essentially 100%
enantiomeric excess" means an enantiomeric excess of at
least 98~ of one of the members of an enantiomeric pair.
The term "ee" is an abbreviation for "enantiomeric
excessn.
The term ~enantiomeric pair" refers to a pair of
substances whose molecules are nonidentical mirror images.
The term "hydrocarbon~ as used herein in referring
to a suitable solvent refers to C 3 to C 8 straight or
branched chain or cyclic hydrocarbons, i.e. pentane, hexane,
cyclooctane, isobutane and the like, and aromatic
hydrocarbons such as benzene or toluene.
The term "alkali metal" includes sodium, lithium
and potassium.
The term "ether" refers to dialkyloxides including
cyclic derivatives such as diethyl ether, tetrahydrofuran
and dimethoxyethane.
The term "R*n refers to an optically active I (+)
or (-)1 substituted or unsubstituted, cyclic or acyclic
alkyl groups having from 4 to 30 carbon atoms~ Acyclic alkyl
geoup may be straight or branched chain. Aryl groups may be
present.
The term "chiral~, as used herein, refers to
compounds which lack reflection symmetry, i.e., are not
identical with their mirror images.
~.'`

~26553~;
-12-
The ter~ ~alkene" refers to acyclic and cyclic
alke~es having ~p to 30 carbon atoms.
The term ~alkyl" refers to ~ub~tituted and
unsubstituted, cyclic and acylic alkyl groups having up to
30 carbon atoms. In the case of acyclic alkyl, the alkyl
groups may be straight or branched chain.
Generally speaking, recrystallization of the solid
borane intermediate, obtained either directly from reacting
a trans- or tertiarY--alkene with monoisopinocampheylborane
or a cis-alkene with diisopinocampheylborane or, when the
reaction product is a liquid, converting the liquid borane
into a solid borate, borane complex or chelate as described
above, is achieved by treatment with a suitable ~ol~ent at
temperatures of from -78C to about 37c, preferably from
0C to -78C and most preferably from about -25c to -~8C.
h'hile concentration of the solute is not critical, it is
generally preferred to use at least 1 molar concentration of
solute or higher.
Suitable cooling baths for recrystallization
include, for exa~lple, pentane slush, dry ice and acetone,
dry ice and alcohol, and the like.
The process of this invention resolves at a stage
where the resulting optically pure intermeàiate can be
employed to prepare a wide variety of final products having
the optical configuration of the optically pure intermediate
as shown in the following general reaction scheme:
'

126553~
DIE~ES (ci s, ci s )
R* CH=CHCH=CHR
R * \ / HR'
\ R~)H / * ~N
~ ~_
,/~7/// ~ \ \~RC
RCHRC02~t 7 RC~2C02~t
RCH2COR ' *
RR2COH
wherein ~ is an optically pure acylic or cyc~ic, sUbstitl~ted . ..
or unsubstituted alkyl group.
~ . .

1~65536
-14-
The following examples further illustrate this
invention.
In the followîng examples, all operations were
carried out under a nitrogen atomosphere with oven-dried
glassware. Gas chromatography analyses were carried out with
a Hewlett-Packard 5750 chromatograph using either (a) a 6 ft
x 0.25 in. column packed with 10% Carbowax*20 M polyethylene
glycol (Union Carbide) on Chromosorb*W(60-80 mesh) aluminum
oxide support or (b) a 6 ft x 0.25 in. column packed with
20% SE-30*~ilicon oil on Chromosorb* ~ (60-80 mesh) aluminum
oxide support. For preparative gas chromotagraphy, eith~r a
(c) 6 ft by 0.5 in. column packed with 10~ Carbowax* 20 M
polyethylene glycol on Chromosorb* W (60-80 mesh) aluminum
oxide support, or a (d) 6 ft x 0.5 in. column packed with
20~ SE-30 silicon oil on Chromosorb*W(60-80) were used.
11 B NMR were recorded ~n a Varian FT-80A*instrument.
The chemical shifts are in ~ relative to the EE-BF3.
Optical rotations were measured on a Rudolph pvlarimeter
Autopol III.
The bis adduct of monoisopinocampheylborane with
tetramethylethylenediamine (TMED.2BH2Ipc) was prepared from
(~)-a-pinene of 91.6% ee according to the reported procedure
of Brown, H.C. et al., J. Org. Chem. 1978, ~43, 5074.
Anhydrous ethyl ether was purchased from Mallinckrodt, Inc.
The alkenes employed in the following examples were
commercial products of the highest purity available. Lithium
aluminum hydride in ethyl ether was purchased f~om Aldrich
Chemical CD.
The optically pure organoboranes provided by this
invention are represented by the formulae:
IpcB~* and Ipc2BR*
wherein Ipc i8 isopinocampheyl and X* i8 an optically active
(I) or ~-) alkyl group~ -
* tradc mark
' ~?`

1;~6553~
-15-
Example 1
Generation of Monoisopinocampheylborane from the
Bis-adduct of Monoisopinocampheylborane with
TetramethYlethYlenediamine in Ethyl Ether
A 250 ml flask with a magnetic stirring bar and
septum was charged with 20.85 g of TMED.ZBH Ipc (50 ~mol)
and ethyl ether ((67.2 ml). While the slurry was stirred at
24C, 12 ml (98 mmol) of boron trifluoride etherate (EE.BF3)
was added dropwise and the reaction mixture was allowed to
stir at 25C for 2 hours. Meanwhile, a 250 ml flask with a
septum inlet, magnetic stirring ~ar and a filtration chamber
was assembled under dry nitrogen and cooled to 25C. The
resulting slurry from the reaction flask was transferred
under nitrogen to the filtration chamber. The solid TMED.2BF
was washed with ethyl ether (2x 36 ml). The combined
filtrate was analyzed for monoisopinocampheylborane by
hydrolysis with 1:1:1 glycerol, water and tetrahydrofuran as
the hydrolyzing mixturelland found to be 0.723 M, 110 ml
(79.5 mmol), 79% yield. B NMR (decoupled): ~22.4(singlet);
~]23D -39.93 (c 11.6, ethyl ether). The standard solution
of monoisopinocampheylborane in ethyl ether can be stored at
0C for at least 20 days without any isomerization or loss
of hydride activity.
Example 2
Preparation of Isopinocampheyl-(lS,2S)-trans-2-Methyl-
cycloPentYlborane
A 50 ml centrifuge vial fitted with a rubber
septum and a magnetic stirring bar was charged with 34.6 ml
of ~-) monoi~opinocampheylborane (lOO~ee) in ethyl ether
(0.723 M, 25 mmol) and cooled to -35C. l-Methylcyclopentene
(3.2 ml, 30 mmol) was added and the reactants were
thoroughly mixed together and the vial left at -35C,
without stirring, for 12 hours. The supernatant solution was

~26~;S3~
-16-
decanted using a double-ended needle. The crystalline
isopinocampheyl- (lS, 2S)-trans-2-methylcyclOpentylborane
was washed with cold (-35C) ethyl ether (2x5 ml) and dried
at 25C under reduced pressure (12 mm Hg~; 3.79 9 (16. 3
mmol, 65~ yield). The dialkylborane was methanolyze~oxidized
and worked up following the literature procedure of Brown~
H.C. et al., J. Or~_ Chem., 1978, 4~, 5074. The
(lS,2S)-trans-2-methylcyclopentanol obtained was purified
using column d to furnish a GC-pure material: [~ ~+46.8
(neat), 100~ ee.
Example 3
Preparation of Isopinoc~npheyl-(2S,3R)-
3-phenvl-2-pentvlborane
Following the procedure of Example 1, 4 ml (25
mmol3 of 1Z]-3-phenyl-2-pentene was added to 27.2 ml (2
mmol) of 0.92 M monoisopinocampheylborane in ethyi ether a~
-35C. The final molarity of the reaction mixture was O.~M
The reactants were mixed well and allowed to stand at -35C,
without stirring, for 12 hours. The impure dialkylborane
crystallized from the solution. The supernatant solution
containing the optically pure dialkylborane was decanted.
The solid was washed with cold ethyl ether (2 x 3 ml) and
dried to yield 1.68 9 of product (5.7 mmol, 22.8& yield)~
The supernat~nt solution was methanolyzed, oxidized ~d
worked up according to the procedure o~ ~rown, H.C. e~ ~ ,
J. Org. Chem., 43, 5074 (1978). The ~2S,3S)
-3-phenyl-2-pentanol obtained was purified using column d to
provide a GC-pure sample: I~] D~24.9 (c 4, C2HsOH~, lO~
ee.

12~S~
-17-
Example 4
Preparation of Isopinocampheyl-(lS,2S)~trans-2-
methylcyclohexylborane
Following the procedure of Example 1, 3.5 ml (30
mmol) of l-methylcyclohexene was added to 34.6 ml (25 mmol)
of 0.723 M monoisopinocampheylborane in ethyl alcohol at
-35C. The reactants were well mixed together annd left at
-35C, without stirring, for 12 hours. The crystalline
dialkylborane was isolated, washed with cold (-35C) ethyl
alcohol (2x5 ml) and dried to yield 5.24 g ~21.3 mmol, 85%
yield) of 89% optically pure dialkylborane. ~he material was
then suspended in 16 ml of tetrahydrofuran so as to give a
1.0 M slurry and allowed to age for 12 hours at 0C. The
supernatant solution was decanted using a double-ended
needle. The solid isopinocampheyl-(lS,2S)
-trans-2-methylcyclohexylborane was washed with cold (0C)
ethyl alcohol (2 x 3 ml) and dried to yield 4.66 g (18.9
mmol, 75~ yield). The dialkylborane was methanolyzed,
oxidized and worked up following the methvd of Brown, H.C.
et al, J. Org. Chem 1981, 46, 2988. The resulting
(lSr2S)-trans-methylcyclohexanol was purified using column d
to furnish a gas chromotagraphy pure sample: [~ 3D ~42.9 (
0.1) c 1, MeOH), ? 99% optical purity.
Example 5
Preparation of Isopinocampheyl-[S]-3-methyl-2-
butylborane
Following the method of Example 1, 3.2 ml (30
mmol) of 2-methyl-2-butene was added to 34.6 ml (25 mmol) of
0.723 M monoi50pinocampheylborane in ethyl alcohol at -35C.
The reactants were mixed together and left at -35C,
. . .
. . .

553~i
-18-
without stirring, for 12 hours. The crystalline diborane was
isolated, washed with cold ~-35C) ethyl ether (2 x 3 ml)
and dried to yield 3.97 9 of product (18 mmol, 72~ yield).
The dialkylborane was 89~ optically pure. It was cooled to
-35~C and 18.5 ml of tetrahydrofuran was added to it so a~
to give a 0.8 M slurry. The reaction mixture wa~ then
allowed to age for 12 hour~ at -35C. The super n a ta n t
solution was decanted using a double-ended needle. T~e ~olid
isopinocampheyl-[SI-3-methyl-2-butylborane was washed with
cold (-35C) ethyl ether and dried to yield 2.82 9 (12.8
mm~l, 51~ yield) of product. The 3-methyl-2-butanol,
obtained following alkaline hydrogen peroxide oxidation
according to the method of Brown, H C. et al. J. Org Chem.
43, 5074 (1978), was purified using column d to give a yd6
chromotagraphy pure material: 1~]23 D +4.97 + 0.01 (neat),
100~ optical purity.
Example 6
Preparation of Dimethyl Alkylbor~nate Esters
of Hiqh Optical Puritv
(lS,2S)-(+)-Dimethyl-trans--methyl-cyc` -
pentylboronate was obtained by adding acetaldehyde (4 ml,
75mmol) to a suspension of isopinocampheyl- tls~2s)-trans- 2
-methylcyclopentylbor~nate prepared by the method of Example
2 (25 mmol) in 20 ml of ethyl ether at 0C. After the
vigorous initial reaction, 2 ml of acetaldehyde was added
and the reaction mixture was ~tirred at 25C for 6 hour~.
Water (Sml) was added and stirred for 0.5 hour. ~xce6s
acetaldehyde was evaporated (25C, 12 n~ Hg, 1 b) and
pentane (30 ml) was added. The boronic acid was extract~d
with 3 M sodium hydroxide ~3 x lS ml) in a separating
funnel. The combined aqueous phase was cooled to 0C,
acidified with a 3 M hydrochloride acid, extract~d with ethyl
~`f!:i``

~S53~i
~19-
ether (3 x 25 ml) and dried over anyhydrous magnesium
sulfate. Ethyl ether was evaporated and the boronic acid was
reesterified with methanol following the procedure of Brown,
H. C., et al., Organometallics 2, 1311 (1983.) The resulting
ester was purified by distilla~ion to yield 2.73 g (70%
yield) bp 72-74C (16 mm Hg); ~] D ~51.56 (c 1, MeOH~,
99% optical purity.
Example 7
Preparation of trans-~2-Methylcyclopentyl)boronate
and trans-2-Methylcyclopentanol of 100% ee
A 50 mL centifuge vial vitted with a rubber septum
and a magnetic stirring bar was charged with 34.6 mL of
(-)-~onoisopinocampheylborane ~IcpBH, 100% ee) in ethyl
ether (0.723 M, 25 mmol) and cooled to _35C.
l-Methylcyclopentene (3.2 mL, 30 mmol) was added to it. The
reactants were mixed together well and the vial was left at
-35C without stirring for 12 hours. The supernatant
solution was decanted with the use of a double-ended needle.
the crystalline is~pinocampheyl-trans-(2-methylcyclo-
pentyl)borane was washed with cold (-35C) ethyl ether (2 x
5 mL) and dried at 25C under reduced pressure (12 mm Hg),
3.79 9 (16.3 mmol, 65~ yield). The dialkylborane was
methanolized, oxidized and worked up following literature
procedures. ~he trans-2-methylcyclopentanol obtained was
purified by using column d to furnish a GC-pure material:
[ a]25D~46.g(neat), 100% ee. The intermediate ~pCR*B~3 was
converted into dimethyl trans-(2-methylcyclopentyl)bor-
onate, bp 85C at 0.05 mm, [~]25D +32.9 (c 7.8, THF), lQ0%
ee.

-20 36
Example 8
Preparation of Dimethyl-trans-(2-MethylCyClOheXyl)bOronate
and trans-2-Methylcyclohexanol in 100~ ee
.
With the experimental set up of Example 7, 3.5 mL
(30 mmol) of l-methylcyclohexene was added to 34.6 mL (25
mmol) of 0.723 M monoisopinocampheylborane in ethyl et~er at
-35C. The reactants were mixed together well and lefs at
-35DC without stirring for 12 hours. The crystalline
dialkylborane was isolated, washed with cold ~-35C) ethyl
ether (2 x 5 mL) and dried t3 provide 5-24 9~21-3 mmol), 85
yield). the dialkylborane wa 89~ optically pure. It wa~
suspended in 16 mL of tetrahydrofuran so as to give a 1.0~
slurry and allowed to age for 12 hours at 0C. ~be
supernatant solution was decanted with use of a double-el~ded
needle. The solid isopinocampheyl-trans-(2-methylcyclo-
hexyl)borane was washed with cold (0C) ethyl ether (2 Y 3
mL) and dried, 4.669 (1~.9 mmolO 75~ yield). The
dialkylborane was methanolized, oxidized and worked up
following the literature prccedure- The trdns-2-methyl-
2 cyclohexanol obtained was purified on column d to furni~h a
GC-pure sample: ¦]23D+42.9O (~ 0.1) (c 1, MeOH), 99~ ee.
The intermediate IpcR*BH was converted into
dimethyl trans-(2-methylcyclohexyl)boronate~ bp 80-81C at
15 mm, l~]23D+41.5C (c 15.4 in THF),'99~ ee.
Example 9
Preparation o~ dimethyl 2-butylboronate and 2-butanol
of 100~ ee
_
Diisopinocampheyl-sec-butylborane was prepared
following the method of H.C. Brown et al, JACS ~6, 397
~0 (1964). Oxidation with alkaline hydrogen peroxide of an
aliquot of this material gave 2-butanol of 95-98~ ee. The
,~i

1265~36
-21-
tetrahydrofuran solvent was removed and the diisopino-
campheyl-sec-butylborane dissolved in pentane. On cooling to
-78C, pure white crystals were obtained. The
crystallization was repeated 5 times. An aliquot of the
final product was oxidized. It revealed l~]25D~5.35O (neat,
~ = 0.5) for 2-butanol. The product was treated with
formaldehyde to form dimethyl 2-butylbor~nate, bp 38~C at 30
mm, l~]23 D 9.1 (c, 12.0 in ~H~), 100% ee.
Example 10
Preparation of 2-Cyclohexenol of 100% ee
-
Diisopinocampheylb~rane was prepared by the method
of H.C. Brown et al., Israel J. Chem. 15, 12 ~1977) from
(+)- ~ -pinene. To the stirred suspension of diisopino-
campheylborane (25mmol) in tetrahydrofuran at -25~C was
added dropwise 2.4 mL (25 mmol) of 1,3-cyclohexadiene.
Monohydroboration of the diene was complete after stirring
the reaction mixture at -25C fGr 12 hours, as indicated by
the disappearance of the solid diisopinocampheylborane and
llB NMR (~ ~B0) examination of the solution. The reaction
mixture was oxidized with trimethylamine-N-oxide, giving a
92:8 mixture of (-)-2-cyclohexen-1-ol (94~ ee) and
3-cyclohexen-1-ol. A second reaction mixture at -78~C was
treated with 25 mm of lithium tert-butyl. Isobutylene was
formed and the organoborane was converted into the
corresponding borohydride as represented by the following
reaction scheme.
~,'`~........... '

~2~553~
-22-
The solution was taken to room temperature and the solvents
removed under vacuum. Dry pentane was added to dissolve the
salt. On c~oling to low temperature, a crystalline product
separated. The product was collected, redissolved in ethyl
ether, and treated with hydrogen chloride to regenerate the
organoborane
_ _ Li
~ ~Li-t-Bu - S ~ BIp ~
The organoborane was oxidized with trimethylene-N-oxide to
yield (-)-2-cyclohexen-1-ol of greater than 99~ ee.
Example 11
Preparation of 2-butyl-1,3,2-dioxaborinane and
2-butanol in 100~ ee
.
To a stirred suspension of 9.26 9 of
diisopinocampheylborane (32.3 mmol) containing a slight
excess of ~-pinene (4.8 mmol) in tetrahydrofuran (30mL) at
-25C was added 35 mmol of cis-butene. The reaction mixture
was stirred at -25C for 12 hours. (Oxidation of a duplicate
reaction mixture gave 2-butanol of 95~ ee.) Then 6.4 mL
(64.6 mmol) of benzaldehyde was added and the mixture
maintained at 0~C. An additional portion of benzaldehyde
(6.4 mL, 64.6 mmol) was added and the reaction mixture
brought to 25C and maintained there for 2 days. llB NM~

~265~36
-- 3--
revealed the borinate:boronate ratio was 30:70. ~ater (5.5
mL) was added and the tetrahydrofuran removed at reduced
pressure. To the residue 20mL of n-pentane was added and the
solution extracted with 3 N NaOH ~3x 11 mL)- The alkaline
extracts were acidified with 6 N HCl ~nd the agueou
solution extracted with ethyl ether ~3x 25 mL)- The ether
extracts were dried over magnesium sulfate and the ether
removed at reduced pressure- There was obtained 2.3 9 of
2-butylborOnic acid. This was treated with 2 mL of
1,3-propanediol in 15 mL of n-pentane. Water separated. The
pentane layer was dried over magnesium ~ulfate. The &ol~ent
removed and the boronic ester, 2-98 9 (21 mmol) was
distilled: bp 64-65C at lS mm, 1~ D -4.7 + 0.03 (c 7,
THF), 100~ ee. Oxidation of the boronic ester produced
2~butanol, [~]23D -10.7C (neat,~ -1.0),
Example 12
Preparation of 3-hexyl-1,3,2-dioxaborinane and 3-heyan
of 100~ ee
_
cis-3-Hexene (32 mmol) was hydroborated by 31 ~mol of
diisopinocamphylborane at -25C following the procedure of
Example 3. lOxidation of a duplicate reaction mixture gives
3-hexanol of 93~ ee). To the reaction mixture at -25DC 63
mmol of acetaldehyde was added, followed by an additi~nal 62
mmol at -5C. The reaction mixture was brought to 25C and
stirred for 72 hours. Then an additionâl 126 ~ol of
acetaldehyde was added- (The aldehyde undergoes a slow
polymerization and is lost to the reaction.) After 1~ days,
the ràtio of borinate:boronate was 40:60 ~ 1 B NMR).
TetrahydrofUran and excess aldehyde was remo~ed under
reduced pressure and 30 mL of n-pentane ~dded to dissolve
the reaction product- The pentane solution was e~tracted
~r
~.~

~26553~
-24
with 3 N NaO~ (4 x 8 ml). The combined alkaline extracts
were acidified with 6 M hydrochloric acid. The white boronic
acid was taken up from the aqueous ~uspension with ethyl
ether (2 x 30 mL). Treatment with trimethylene glycol in
pentane gave a 70~ yiel~ of the ester, 2-hexyl-1,3,2- diO~a-
borinane, bp 92-94 (15mm), 1~ D +0.87l 0.01 (c lS, T~F).
Oxidation with alkaline hydrogen peroxide gave 3-hexanol,
[~ D-7.50 (neat), >99~ ee.
Example 13
lQ Preparation of dimethyl l+)-exo-Norbornylboronate and
(-)-exo-Norborneol
In the usual reaction vessel under nitrogen, 33
mmol of norbornene was hydrobo~ated at -25C with 33 mmol of
diisopinocampheylborane in tetrahydrofuran (26 mL) in the
presence of a slight excess of ~-pinene (4 9 mmol). The
reaction product was trea~ed with acetaldehyde; 66 mmol was
added at -25C and an additional 66 mmol was added at ~C.
The reaction mixture was then stirred for 2 days at 25C.
After 2 days, the borinate:boronate ratio was 45:55 ( 11~
NMR). The tetrahydrofuran and excess ace~aldehyde was
removed under reduced pressure. n-Pentane (35 mL) was added
and the pentane ~olution was extracted with 3 M NaOH (4 x 11
mL). The alkaline extract was acidified with 6 M HCl. The
boronic acid separated. It wa~ extracted with ethyl ether (3
x 25 ml). The recovered acid was esterified by methanol to
produce dimethyl exo-norbornylboronate, bp 82-84~C at 15 n~.
Oxidation with alkaline hydrogen peroxide produced 1.7 9 of
(-)-exo-norbornanol, pur if ied by preparatiYe gas
chromotography~ 3 D-4.9, g7~ ee ~determined by the 31p
NMR of the phosphate ester. Reaction of dimethyl-(+)-exo-
norbornylboranate with N,N,N,N-tetrakis-
(2-hydroxyethyl)ethylenediamine producefi the corresponding

1265S36
-25-
solid ester. After several recrystallizations, exo-
norbornyl boronic acid was recovered in 100% ee
Example 1~
Preparation of N,N,N,N-Tetrakis(2-hydroxyethyl)-
ethylenediamine Ester of Tetrahydro-2H-3-pyranylboronate
and (+)-3-Hydroxytetrahydro-2H-pyran of 100% ee
.
To diisopinocampheylborane of high optical purity
(25 mmol) in tetrahydrofuran, 2.3 mL (25 mmol) of
dihydropyran (kept over anhydrous potassium carbonate
1~ overnight and distilled) was added dropwise at 0C and kept
under magnetic stirring for 12 hours. By that time, the
solid diisopinocampheylborane had disappeared. 11~ NMR of
the reaction mixture showed a signal corresponding to
trialkylborane ( ~ 87). To this, 5.6 mL ~100 mmol, 6~
excess) of acetaldehyde was added and stirred at 25C for 6
hours. 11B NMX of the reaction mixt~re showed a peak
corresponding to boronate ( ~29.7). Excess acetaldehyde was
removed under vacuum (30 mm Hg). The boronate thus obtained
could not be distilled, as it decomposed upon heating. The
reaction mixture was oxidized using 25 ml of 3 N sodium
hydroxide and 3.75 mL of 30% hydrogen peroxide at 25C for 5
hours. To the crude reaction mixture 25 9 of anhydrous
potassium carbonate was added and the organic layer was
separated. The aqueous layer was extracted with 3 x 15 ml
of ether. The combined organic layer was washed with
saturated sodium chloride solution and the organic layer wa~
dried over anhydrous magnesium sulfate. Ether was
evaporated. The crude reaction mixture was filtered through
silica gel (column chromotagraph). Pentane eluents removed
the ~ -pinene and the ether eluents yielded
3-hydroxytetrahydropyran. The alcohol was distilled to
obtain (99% chemically pure) 2.012 g of pure sample, bp

l~S53~
-26-
90C/20 mm, n D 1.4570. Yield: 80%. It was further purified
by preparative yas chromotograph (20~ Carbowax*20M, 12~C~
to obtain 100% chemically pure sample: l~] D~10.55(neat).
Its optical purity was determined by 19 F NMR
technique by making its Mosher ester in the usual manner:
86% ee. The optical purity of the boronic acid was upgraded
to 100% by recrystallization of the 2:1 chelated ester
formed by esterification with N,N,N,N-tetrakis-
(2-hydroxyethyl)ethylenediamine as described in Example 15
below.
Example 15
Preparation of 3-Hydroxy-2~-Tetrah ~ropyran of 100~ ee
-
Ethyl tetrahydro-2H-3-pyranyl boronate (crude),
was prepared as described above in Example 14. ~-Pinene was
displaced by treatment with ~ aldehyde and removed under
vacuum at 0.5 mm of mercury for 6 hours. The boronate thus
obtained was free from ~-pinene. To it (25 mmol) 25 mL of
ether, followed by 2.95 9 of N,N,N,N-ethylenediamine-
tetraethanol in 15 ml of isopropanol was added and stirred
at 25C for 1 hour. A white solid was crystallized out. It
was filtered to obtain 5.5 9 of boronate. Yield: 52~
(starting from olefin). B NMR: ~ 37.2, mp 81C. The solid
was taken in 13 mL of ether and to it 13 mL of 2 N
hydrochloric acid was added and stirred at 24C for 0.5
hour. The ether layer was removed by a double-ended needle
and the aqueous layer was saturated with sodium chloride and
extracted with 3 x 10 mL of ether~ The combined organic
layer was dried over anhydrous magnesium sulfate and the
ether pumped off. A while crystalline solid,
tetrahydro-2H-pyranylboronic acid was obtained. It was taken
in Z0 ml of ether and oxidized with 3 N sodium hydroxide and
30% hydrogen peroxide. 3-Hydroxy-2H-tetrahydropyran thus
* trade mark

~26S536
-27-
obtained was distilled and further purified by preparative
gas chromotagraphy to obtain 100 ~ chemically pure sample~
l~ D +11.93C (neat), 100~ ee by 19F NMR.
The above procedures were all carried out under
nitrogen. For consistency, all reactions used (~ pinene,
The use of (~ pinene gives products of the OppOSite
rotation and the enantiomeric isomer.

Dessin représentatif